The present invention relates to a multimode monitor and, more particularly, to a mode detector of a multimode monitor, which detects a frequency mode applied to the multimode monitor and provides a mode signal to control the multimode monitor.
As the technology related to a computer has been developed, horizontal and vertical frequency bands are more varied. In a VGA (video graphic array) mode, the vertical frequency is generally 60 Hz or 70 Hz and the horizontal frequency is 31.5 KHz. Also, in an extended VGA mode, each horizontal and vertical frequency is 35.5 KHz and 86 Hz, respectively. Recently, in a strong VGA mode, 56 Hz or 60 Hz is used as the vertical frequency and 35.5 KHz or 37.5 KHz is used as the horizontal frequency. Thus, the multimode monitors are required to convert the mode according to various horizontal and vertical frequencies.
FIG. 1 shows an example of a conventional multimode monitor. In the conventional multimode monitor, the input vertical and horizontal frequency signals are converted to a constant voltage level by a vertical frequency-to-voltage converter 10 and a horizontal frequency-to-voltage converter 20, respectively.
According to output voltages of the vertical and horizontal frequency-to-voltage converters 10 and 20, vertical and horizontal frequency band separators 60 and 30 distinguish bands of respective input vertical and horizontal frequencies to control vertical and horizontal switching circuits 70 and 80, respectively. Then, the vertical and horizontal switching circuits 70 and 80 change respective internal oscillating vertical and horizontal frequencies according to the input vertical and horizontal frequencies. In such multimode monitors, the internal oscillating vertical and horizontal frequencies are respectively synchronized with by the input vertical and horizontal frequencies to focus a screen synchronously with the input frequencies.
However there is a problem that vertical and horizontal sizes, positions, and horizontal pin cushion should be controlled accurately according to the input vertical and horizontal frequency modes so that those are to be controlled manually by users.